Background: Preterm birth is associated with socio-cognitive dysfunction, which is currently not monitored in routine early follow-up of these infants. Face recognition plays an important role in early socio-cognitive development but may be impacted by the use of face masks. Functional near-infrared spectroscopy (fNIRS) measures the cerebral hemodynamic response to neural stimuli. Objective: We aimed to assess face recognition and the impact of face masks in preterm and term infants using fNIRS. Design/Methods: Preterm (born at 24-26 weeks’ gestational age, n=4) and term infants (n=5) were studied at the post-term age of 6 months. The infants viewed images of smiling faces in full view or with a surgical face mask. The task comprised of alternating 5-s experimental trials each displaying a sequence of 5 full or masked faces. Experimental trials were interspersed with baseline trials of 9-15s displaying pictures of houses at 1Hz. The cerebral haemodynamic response function was measured using multichannel fNIRS (BRITE, Artinis) over the inferior-frontal, temporo-parietal, and lateral occipital regions (18 channels over both hemispheres, based on the 10/20 system). The brain response to the visual stimuli was calculated as changes in the oxy- and deoxyhaemoglobin concentration (ΔHbO and ΔHbR, µM). A Wilcoxon test was used to compare the full and masked face conditions, and a Mann-Whitney U test was used to compare term and preterm groups. Results: In term infants, the peak ΔHbO showed a trend of being reduced for masked faces compared to full faces over all regions in the right brain, with near-significance (p = 0.055) in the P6-P8 channel (10/20 system) in the temporo-parietal region. In contrast in preterm infants, this trend was not observed. No difference between term and preterm infants was found for the ΔHbO response to full faces, but preterm infants had a higher peak ΔHbO in the right occipital region for masked faces compared to term infants (0.30 [0.24-0.55] vs. 0.13 [0.04-0.21] µM; p = 0.029). Neither preterm nor term infants demonstrated differences between full and masked faces in the left hemisphere.
Conclusion(s): The right brain in 6-month-old term, but not preterm, infants showed reduced neural activation when watching masked faces, compared to full faces. The cerebral response differs between term and preterm infants in the right occipital region, suggesting different neural processing and activation in preterm infants when watching masked faces. This is of particular relevance given face masks are still used in most hospitals.
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